/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_dct4_q15.c
*
* Description:	Processing function of DCT4 & IDCT4 Q15.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @addtogroup DCT4_IDCT4
 * @{
 */

/**
 * @brief Processing function for the Q15 DCT4/IDCT4.
 * @param[in]       *S             points to an instance of the Q15 DCT4 structure.
 * @param[in]       *pState        points to state buffer.
 * @param[in,out]   *pInlineBuffer points to the in-place input and output buffer.
 * @return none.
 *
 * \par Input an output formats:
 * Internally inputs are downscaled in the RFFT process function to avoid overflows.
 * Number of bits downscaled, depends on the size of the transform.
 * The input and output formats for different DCT sizes and number of bits to upscale are mentioned in the table below:
 *
 * \image html dct4FormatsQ15Table.gif
 */

void arm_dct4_q15(
    const arm_dct4_instance_q15* S,
    q15_t* pState,
    q15_t* pInlineBuffer)
{
	uint32_t i;                                    /* Loop counter */
	q15_t* weights = S->pTwiddle;                  /* Pointer to the Weights table */
	q15_t* cosFact = S->pCosFactor;                /* Pointer to the cos factors table */
	q15_t* pS1, *pS2, *pbuff;                      /* Temporary pointers for input buffer and pState buffer */
	q15_t in;                                      /* Temporary variable */


	/* DCT4 computation involves DCT2 (which is calculated using RFFT)
	 * along with some pre-processing and post-processing.
	 * Computational procedure is explained as follows:
	 * (a) Pre-processing involves multiplying input with cos factor,
	 *     r(n) = 2 * u(n) * cos(pi*(2*n+1)/(4*n))
	 *              where,
	 *                 r(n) -- output of preprocessing
	 *                 u(n) -- input to preprocessing(actual Source buffer)
	 * (b) Calculation of DCT2 using FFT is divided into three steps:
	 *                  Step1: Re-ordering of even and odd elements of input.
	 *                  Step2: Calculating FFT of the re-ordered input.
	 *                  Step3: Taking the real part of the product of FFT output and weights.
	 * (c) Post-processing - DCT4 can be obtained from DCT2 output using the following equation:
	 *                   Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)
	 *                        where,
	 *                           Y4 -- DCT4 output,   Y2 -- DCT2 output
	 * (d) Multiplying the output with the normalizing factor sqrt(2/N).
	 */

	/*-------- Pre-processing ------------*/
	/* Multiplying input with cos factor i.e. r(n) = 2 * x(n) * cos(pi*(2*n+1)/(4*n)) */
	arm_mult_q15(pInlineBuffer, cosFact, pInlineBuffer, S->N);
	arm_shift_q15(pInlineBuffer, 1, pInlineBuffer, S->N);

	/* ----------------------------------------------------------------
	 * Step1: Re-ordering of even and odd elements as
	 *             pState[i] =  pInlineBuffer[2*i] and
	 *             pState[N-i-1] = pInlineBuffer[2*i+1] where i = 0 to N/2
	 ---------------------------------------------------------------------*/

	/* pS1 initialized to pState */
	pS1 = pState;

	/* pS2 initialized to pState+N-1, so that it points to the end of the state buffer */
	pS2 = pState + (S->N - 1u);

	/* pbuff initialized to input buffer */
	pbuff = pInlineBuffer;


#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	/* Initializing the loop counter to N/2 >> 2 for loop unrolling by 4 */
	i = (uint32_t) S->Nby2 >> 2u;

	/* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
	 ** a second loop below computes the remaining 1 to 3 samples. */
	do {
		/* Re-ordering of even and odd elements */
		/* pState[i] =  pInlineBuffer[2*i] */
		*pS1++ = *pbuff++;
		/* pState[N-i-1] = pInlineBuffer[2*i+1] */
		*pS2-- = *pbuff++;

		*pS1++ = *pbuff++;
		*pS2-- = *pbuff++;

		*pS1++ = *pbuff++;
		*pS2-- = *pbuff++;

		*pS1++ = *pbuff++;
		*pS2-- = *pbuff++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);

	/* pbuff initialized to input buffer */
	pbuff = pInlineBuffer;

	/* pS1 initialized to pState */
	pS1 = pState;

	/* Initializing the loop counter to N/4 instead of N for loop unrolling */
	i = (uint32_t) S->N >> 2u;

	/* Processing with loop unrolling 4 times as N is always multiple of 4.
	 * Compute 4 outputs at a time */
	do {
		/* Writing the re-ordered output back to inplace input buffer */
		*pbuff++ = *pS1++;
		*pbuff++ = *pS1++;
		*pbuff++ = *pS1++;
		*pbuff++ = *pS1++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);


	/* ---------------------------------------------------------
	 *     Step2: Calculate RFFT for N-point input
	 * ---------------------------------------------------------- */
	/* pInlineBuffer is real input of length N , pState is the complex output of length 2N */
	arm_rfft_q15(S->pRfft, pInlineBuffer, pState);

	/*----------------------------------------------------------------------
	 *  Step3: Multiply the FFT output with the weights.
	 *----------------------------------------------------------------------*/
	arm_cmplx_mult_cmplx_q15(pState, weights, pState, S->N);

	/* The output of complex multiplication is in 3.13 format.
	 * Hence changing the format of N (i.e. 2*N elements) complex numbers to 1.15 format by shifting left by 2 bits. */
	arm_shift_q15(pState, 2, pState, S->N * 2);

	/* ----------- Post-processing ---------- */
	/* DCT-IV can be obtained from DCT-II by the equation,
	 *       Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)
	 *       Hence, Y4(0) = Y2(0)/2  */
	/* Getting only real part from the output and Converting to DCT-IV */

	/* Initializing the loop counter to N >> 2 for loop unrolling by 4 */
	i = ((uint32_t) S->N - 1u) >> 2u;

	/* pbuff initialized to input buffer. */
	pbuff = pInlineBuffer;

	/* pS1 initialized to pState */
	pS1 = pState;

	/* Calculating Y4(0) from Y2(0) using Y4(0) = Y2(0)/2 */
	in = *pS1++ >> 1u;
	/* input buffer acts as inplace, so output values are stored in the input itself. */
	*pbuff++ = in;

	/* pState pointer is incremented twice as the real values are located alternatively in the array */
	pS1++;

	/* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
	 ** a second loop below computes the remaining 1 to 3 samples. */
	do {
		/* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */
		/* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */
		in = *pS1++ - in;
		*pbuff++ = in;
		/* points to the next real value */
		pS1++;

		in = *pS1++ - in;
		*pbuff++ = in;
		pS1++;

		in = *pS1++ - in;
		*pbuff++ = in;
		pS1++;

		in = *pS1++ - in;
		*pbuff++ = in;
		pS1++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);

	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
	 ** No loop unrolling is used. */
	i = ((uint32_t) S->N - 1u) % 0x4u;

	while(i > 0u) {
		/* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */
		/* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */
		in = *pS1++ - in;
		*pbuff++ = in;
		/* points to the next real value */
		pS1++;

		/* Decrement the loop counter */
		i--;
	}


	/*------------ Normalizing the output by multiplying with the normalizing factor ----------*/

	/* Initializing the loop counter to N/4 instead of N for loop unrolling */
	i = (uint32_t) S->N >> 2u;

	/* pbuff initialized to the pInlineBuffer(now contains the output values) */
	pbuff = pInlineBuffer;

	/* Processing with loop unrolling 4 times as N is always multiple of 4.  Compute 4 outputs at a time */
	do {
		/* Multiplying pInlineBuffer with the normalizing factor sqrt(2/N) */
		in = *pbuff;
		*pbuff++ = ((q15_t)(((q31_t) in * S->normalize) >> 15));

		in = *pbuff;
		*pbuff++ = ((q15_t)(((q31_t) in * S->normalize) >> 15));

		in = *pbuff;
		*pbuff++ = ((q15_t)(((q31_t) in * S->normalize) >> 15));

		in = *pbuff;
		*pbuff++ = ((q15_t)(((q31_t) in * S->normalize) >> 15));

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);


#else

	/* Run the below code for Cortex-M0 */

	/* Initializing the loop counter to N/2 */
	i = (uint32_t) S->Nby2;

	do {
		/* Re-ordering of even and odd elements */
		/* pState[i] =  pInlineBuffer[2*i] */
		*pS1++ = *pbuff++;
		/* pState[N-i-1] = pInlineBuffer[2*i+1] */
		*pS2-- = *pbuff++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);

	/* pbuff initialized to input buffer */
	pbuff = pInlineBuffer;

	/* pS1 initialized to pState */
	pS1 = pState;

	/* Initializing the loop counter */
	i = (uint32_t) S->N;

	do {
		/* Writing the re-ordered output back to inplace input buffer */
		*pbuff++ = *pS1++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);


	/* ---------------------------------------------------------
	 *     Step2: Calculate RFFT for N-point input
	 * ---------------------------------------------------------- */
	/* pInlineBuffer is real input of length N , pState is the complex output of length 2N */
	arm_rfft_q15(S->pRfft, pInlineBuffer, pState);

	/*----------------------------------------------------------------------
	 *  Step3: Multiply the FFT output with the weights.
	 *----------------------------------------------------------------------*/
	arm_cmplx_mult_cmplx_q15(pState, weights, pState, S->N);

	/* The output of complex multiplication is in 3.13 format.
	 * Hence changing the format of N (i.e. 2*N elements) complex numbers to 1.15 format by shifting left by 2 bits. */
	arm_shift_q15(pState, 2, pState, S->N * 2);

	/* ----------- Post-processing ---------- */
	/* DCT-IV can be obtained from DCT-II by the equation,
	 *       Y4(k) = Y2(k) - Y4(k-1) and Y4(-1) = Y4(0)
	 *       Hence, Y4(0) = Y2(0)/2  */
	/* Getting only real part from the output and Converting to DCT-IV */

	/* Initializing the loop counter */
	i = ((uint32_t) S->N - 1u);

	/* pbuff initialized to input buffer. */
	pbuff = pInlineBuffer;

	/* pS1 initialized to pState */
	pS1 = pState;

	/* Calculating Y4(0) from Y2(0) using Y4(0) = Y2(0)/2 */
	in = *pS1++ >> 1u;
	/* input buffer acts as inplace, so output values are stored in the input itself. */
	*pbuff++ = in;

	/* pState pointer is incremented twice as the real values are located alternatively in the array */
	pS1++;

	do {
		/* Calculating Y4(1) to Y4(N-1) from Y2 using equation Y4(k) = Y2(k) - Y4(k-1) */
		/* pState pointer (pS1) is incremented twice as the real values are located alternatively in the array */
		in = *pS1++ - in;
		*pbuff++ = in;
		/* points to the next real value */
		pS1++;

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);

	/*------------ Normalizing the output by multiplying with the normalizing factor ----------*/

	/* Initializing the loop counter */
	i = (uint32_t) S->N;

	/* pbuff initialized to the pInlineBuffer(now contains the output values) */
	pbuff = pInlineBuffer;

	do {
		/* Multiplying pInlineBuffer with the normalizing factor sqrt(2/N) */
		in = *pbuff;
		*pbuff++ = ((q15_t)(((q31_t) in * S->normalize) >> 15));

		/* Decrement the loop counter */
		i--;
	} while(i > 0u);

#endif /* #ifndef ARM_MATH_CM0 */

}

/**
   * @} end of DCT4_IDCT4 group
   */
